Effects of orbital forcing, greenhouse gases and ice sheets on Saharan greening in past and future multi-millennia

Abstract. Climate archives reveal alternating arid and humid conditions in North Africa during the last several million years. Most likely dry phases resembled current hyper-arid landscapes, whereas wet known as African periods (AHPs) sustained much more surface water greater vegetated areas that “greened” large parts of Sahara region. Previous analyses sediment cores from Mediterranean Sea showed five AHPs differed strength, duration rate change. To understand causes such differences we perform transient simulations past 190 000 years with Earth system model intermediate complexity CLIMBER-2. We analyse amplitude change modelled AHP responses to changes orbital parameters, greenhouse gases (GHGs) ice sheets. In agreement estimates sapropels, find predicts a threshold forcing for greening occurrence AHPs. Maximum rates simulated vegetation extent at onset termination correlate strongly forcing. As suggested by available data Holocene AHP, usually happens faster than termination. A factor separation analysis confirms dominant role driving precipitation Forcing due GHGs sheets is only secondary importance, small contribution synergies Via detect varies GHG levels. explore implication our finding palaeoclimate might occur greenhouse-gas-induced warmer climate, extend into future. For next 100 variations will be smaller millennia, insolation late Quaternary not crossed. However, higher concentrations predicted drops considerably. Thereby, upcoming millennia appears crucially depend on future GHGs.